chore: remove panic usage in keeper methods

[fmorency]

This PR removes the panic usage in keeper methods. This should fix the remaining CodeQL warnings.

Code hygiene following cosmos/cosmos-sdk#18636, cosmos/cosmos-sdk#16212 and cosmos/cosmos-sdk#12985

[codecov]

Codecov Report

Attention: Patch coverage is 47.36842% with 10 lines in your changes are missing coverage. Please review.

Project coverage is 59.69%. Comparing base (6a7913e) to head (e77fe05).

Files	Patch %	Lines
x/manifest/keeper/keeper.go	50.00%	6 Missing and 2 partials ⚠️
x/manifest/abci.go	33.33%	1 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #49      +/-   ##
==========================================
- Coverage   59.86%   59.69%   -0.17%     
==========================================
  Files          34       34              
  Lines        2145     2151       +6     
==========================================
  Hits         1284     1284              
- Misses        802      805       +3     
- Partials       59       62       +3     

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